Utilizing the self-luminous property of organic semiconductor material for displaying, an organic light emitting display (OLED) has the advantages of, among others, high contrast and low power consumption. Typically, the display area of the organic light emitting display is provided with a pixel array composed of pixels and sub-pixels. Each sub-pixel contains an organic light emitting diode, driven by a pixel driving circuit to emit light.
A conventional pixel driving circuit may include a driving transistor which provides a light emitting current to an organic light emitting device under the control of a light emitting control signal. Since the light emitting current of the organic light emitting diode is related to a threshold voltage Vth of the driving transistor, the shifting of the threshold voltage Vth of the driving transistor (i.e., “threshold shift”) due to manufacture, aging after extended use, and other causes will result in the luminance of the organic light emitting device being unstable. In addition, in the conventional pixel driving circuit, the light emitting current of the organic light emitting diode is affected by a capacitance value thereof. Since capacitance values of organic light emitting diodes in different pixel driving circuits may not be the same, even if an identical data signal is provided, the luminances of various organic light emitting diodes will be different, resulting in reduced uniformity for the display luminance. Therefore, a solution for uniform display is needed.